ENGR2000_mechanicalproperties

ENGR2000_mechanicalproperties - Introduction to Engineering...

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Introduction to Engineering Materials ENGR2000 Chapter 6: Mechanical Properties of Metals Dr. Priya Thamburaj Goeser
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6.2 Concepts of Stress and Strain • Principal ways in which a load may be applied –Ten s ion – Compression – Shear – Torsional
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Fracture & Failure •F r a c t u r e occurs when a structural component separates into two or more pieces. fracture represents failure of the component Failure is the inability of a component to perform its desired function. failure may occur prior to fracture e.g. a car axle that bends when you drive over a pothole
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Tension Tests • The specimen is deformed to fracture with a gradually increasing tensile load…
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Engineering Stress & Engineering Strain 0 0 0 0 : strain g Engineerin : stress g Engineerin l l l l Δ l ε A F = = = σ
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Compression Tests • Similar to the tensile tests • Force is compressive • Specimen contracts along direction of the stress
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Engineering Stress & Engineering Strain 0 : strain g Engineerin : stress g Engineerin 0 0 0 0 < = = = l l l l Δ l ε A F σ
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Shear and Torsional Tests () θ γ τ small for tan : strain Shear : stress Shear 0 = = = h w A F
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Shear and Torsional Tests () φ γ τ f T f = = : torque applied to due strain Shear : torque applied to due stress Shear
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Deformation All materials undergo changes in dimensions in response to mechanical forces. This phenomenon is called deformation . If the material reverts back to its original size and shape upon removal of the load, the deformation is said to be elastic deformation . If application and removal of the load results in a permanent change in size or shape, the deformation is said to be plastic deformation .
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Elastic Deformation 6.3 Stress-Strain Behavior ε E E σ ε = = : elasticity of Modulus : law s Hooke' γ τ = G : modulus Shear
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Modulus of Elasticity • Young’s modulus • Elastic modulus • Stiffness • Material’s resistance to elastic deformation – greater the elastic modulus, the stiffer the material or smaller the elastic strain that results from the application of a given stress.
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Elastic modulus of metals, ceramics & polymers •C e r a m i c s – high elastic modulus – diamond, graphite (covalent bonds) • Metals – high elastic modulus •P o l y m e r s – low elastic modulus – weak secondary bonds between chains Increasing E
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Tangent or Secant Modulus • Materials with non-linear elastic behavior – Gray cast iron, – concrete, – many polymers
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Elastic Modulus on an Atomic Scale • Elastic strain – small changes in inter-atomic spacing – stretching of inter-atomic bonds • Elastic modulus – resistance to separation of adjacent atoms – inter-atomic bonding forces
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Review 2.5 Bonding Forces and Energies length. bond the as known is apart. are atoms two the of centers the - 0 : m equilibriu At : force net The 0 0 r r F F F F F F R A N R A N = + = + =
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Elastic Modulus on an Atomic Scale 0 r dr dF E
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Effect of Temperature on the Elastic Modulus
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Example 6.1
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This note was uploaded on 10/24/2009 for the course ENGR 2000 taught by Professor Goeser during the Fall '08 term at Armstrong State University.

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ENGR2000_mechanicalproperties - Introduction to Engineering...

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